Three-way valves have long been used for controlling fluid flow in various types of pneumatic and hydraulic systems over a wide range of applications. In some of these valve assemblies, the valve member is in the form of a ball which is free to move between a pair of valve seats and an actuating pin for urging the ball against one of the two valve seats. This type of ball valve suffers from several limitations, including not being sufficiently precise to control the flow of fluid. In addition, the ball member may occasionally tend to impede the full flow of fluid through a side port when the ball is disposed intermediate the two valve seats.
One type of three-way valve is the block and bleed valve for controlling fluid communication between a pressure source and at least two valves activated by the pressure source. These types of valves are frequently used for controlling fluid flow between a pressure source, a pilot valve, and a safety valve. These types of valves generally include a diaphragm, or partition, disposed between different chamber portions of the valve which operate at different pressures during certain phases of the functioning of the valve. The diaphragm is subject to deterioration which interferes with valve operation and requires frequent replacement. These types of valves also include two separate valves in a manifold: one valve to control access to the source of pressure, and the other valve to allow for draining, or bleed off, of the fluid under pressure. Because these types of valves actually include two inter-dependent valves, they are assembled from many components, require complicated connection schemes, and are subject to error by operating the wrong valve, or only one valve.
The present invention avoids these limitations of the prior art by providing a block and bleed valve assembly having a single movable member, operated by hand or by machine, which is easily and quickly displaced between first and second positions for respectively isolating and connecting a pressure-operated device and a source of either pneumatic or hydraulic pressure. A “soft”, leak-free seal is provided for isolating the source of pressure from the pressure-operated device and the fluid drain, or bleed.